The performance of a gas pressure regulator may be defined by four principal characteristics of the regulator. Namely its flow curve, hysteresis, creep and reproducibility. The flow curve of a regulator expresses the regulator's ability to maintain the outlet pressure of the regulator as the outlet flow changes. Hysteresis refers to the ability of the regulator to maintain the outlet pressure whether the flow is increased from a lower value to a new value or the flow is decreased from a higher value to that new value.
The creep of a pressure regulator, also known as "lock-up", is the ability of the regulator to maintain the outlet pressure as the flow is decreased from a small value to a no-flow condition. The reproducibility of a pressure regulator is an indication of its ability to return to the same operating outlet pressure as the flow goes from zero, the shutoff condition, to the operating steady state value.
It is desirable that the size of a gas pressure regulator, particularly its width, be made as compact as possible so that the regulator occupies minimal space. For example, a plurality of regulators may be arranged side by side in a row in a gas control installation. For a finite row length, which may be determined by existing cabinet size, the proximity of surrounding apparatus, etc., a greater number of pressure regulators can be accommodated if the width of the regulators can be reduced.